The Zbtb family of proteins consists of more than 40 members in mice. They are highly conserved transcriptional repressors that contain a BTB (POZ) protein-binding domain and a Kruppel-type Zinc Finger (ZF) DNA-binding domain. Many members of this family were shown to play essential roles during the differentiation of immune cells. The general goal of this project is to elucidate the contribution of specific Zbtb family members to lymphocyte differentiation and function. To this aim, we are focusing on two transcription factors. a) The role of PLZF in the innate-like differentiation of lymphocytes. iNKT cells are a subtype of lymphocytes with unique characteristics, due to their fast activation response, their cytokine-secreting capabilities and their cytotoxic functions, they can shape immune responses in several pathological conditions such as in infection, autoimmunity and cancer. Previous work from us and others identified that PLZF expression is necessary for the development and acquisition of effector functions in innate-like iNKT cells. Current work from our laboratory identified that PLZF expression is not restricted to innate-like T-cells and that PLZF is also expressed in progenitors of all T-cells in the fetal thymus. Besides this general expression of PLZF in fetal T-cell progenitors, PLZF didn't affect the development of conventional T-cells. Interestingly, PLZF expression was maintained in a subset of gamma-delta T-cells that exclusively develop in the fetus and secrete IL-17. These cells are not gamma-delta NKT cells, which also depend on PLZF for their development. Our results also identified that PLZF was necessary for the development of fetal-derived IL-17-secreting gamma-delta T-cells. We are currently evaluating how PLZF affects the differentiation of this subset of gamma-delta T-cells. b) Another focus of the laboratory is on the role of Zbtb1 in T-cell development. It was recently shown that Zbtb1 expression is necessary for the development of lymphoid but not myeloid cells. Mice mutant or deficient for Zbtb1 lacked T-cells and have a partial developmental defect in B and NK cell lineages. We are evaluating the mechanism by which Zbtb1 specifically affect T-cell development using in vitro as well as in vivo differentiation models. We have observed that absence of functional Zbtb1 in hematopoietic progenitors leads to a preferential differentiation of myeloid cells versus T-cells in vitro. This phenotype was however reversed by retroviral transduction with a bcl2 over expressing vector, which protects cells from apoptosis, indicating that the preferential myeloid differentiation was consequence of increased apoptosis of cells that committed towards the T-cell lineage. We have confirmed these in vitro results by transgenic expression of bcl2 in Zbtb1-mutant mice, which leads to restored T-cell development in vivo. We are currently evaluating the anti-apoptotic function of Zbtb1 in developing thymocytes.